Pub Date : 2024-11-04DOI: 10.1016/j.gete.2024.100608
Josselin Ouf , Kavan Khaledi , Philip J. Vardon , Wen Luo , Mohammadreza Jalali , Florian Amann
This study presents a fully coupled hydro-mechanical framework for modeling hydraulic shearing in a mesoscale reservoir located at the Grimsel Test Site, Switzerland. The experiment was conducted on a ductile–brittle fault embedded in low-permeable granite. We observe that normal fracture opening increases flow channel recoverably, while fracture sliding locks asperities leading to a non-recoverable increase in flow. To couple these processes, we use a poro-elasto-plastic constitutive framework and employ a permeability function that depends on several parameters, such as dilation angle, in-situ stresses, residual aperture and maximum aperture. Our results capture the recorded pressure responses well, and indicate that the permeability changes by one order of magnitude during the experiment.
{"title":"Numerical modeling of hydro-mechanical processes during hydraulic testing of pre-existing fractures at the Grimsel Test Site, Switzerland","authors":"Josselin Ouf , Kavan Khaledi , Philip J. Vardon , Wen Luo , Mohammadreza Jalali , Florian Amann","doi":"10.1016/j.gete.2024.100608","DOIUrl":"10.1016/j.gete.2024.100608","url":null,"abstract":"<div><div>This study presents a fully coupled hydro-mechanical framework for modeling hydraulic shearing in a mesoscale reservoir located at the Grimsel Test Site, Switzerland. The experiment was conducted on a ductile–brittle fault embedded in low-permeable granite. We observe that normal fracture opening increases flow channel recoverably, while fracture sliding locks asperities leading to a non-recoverable increase in flow. To couple these processes, we use a poro-elasto-plastic constitutive framework and employ a permeability function that depends on several parameters, such as dilation angle, in-situ stresses, residual aperture and maximum aperture. Our results capture the recorded pressure responses well, and indicate that the permeability changes by one order of magnitude during the experiment.</div></div>","PeriodicalId":56008,"journal":{"name":"Geomechanics for Energy and the Environment","volume":"40 ","pages":"Article 100608"},"PeriodicalIF":3.3,"publicationDate":"2024-11-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142651374","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-10-29DOI: 10.1016/j.gete.2024.100612
Nima Haghighat, Amir Shoarian Sattari, Frank Wuttke
Understanding and predicting potential failure mechanisms during the excavation and open drift stages of geological repository construction are among the crucial aspects of performance evaluation and safety assessment of nuclear waste storage facilities. The development of the Excavation Damage Zone (EDZ) and the generation of shrinkage-induced cracks during operational phases are prominent examples of failure mechanisms that can compromise the integrity of the repository systems. This study presents an integrated framework for investigating shrinkage-induced cracking of Opalinus Clay in niches and tunnels. To achieve this, the hybrid Finite Discrete Element Method (FDEM) is employed. The methodology incorporates a two-way staggered hydro-mechanical coupling scheme, where solid phase analysis relies on 2D FDEM and fluid flow is modeled using the nonlinear Richards’ equation and solved via Finite Volume discretization. To account for the effects of EDZ, characterized by a pronounced increase in hydraulic conductivity, a numerical simulation of tunnel excavation is first carried out. The resulting failure pattern around underground openings is then abstracted through the definition of an altered hydraulic conductivity field. Comparison of the numerical results with field observations demonstrates the framework’s ability to capture a wide range of failure mechanisms inherent in various stages of underground repository construction in Opalinus Clay.
{"title":"A finite discrete element approach for modeling of desiccation fracturing around underground openings in Opalinus clay","authors":"Nima Haghighat, Amir Shoarian Sattari, Frank Wuttke","doi":"10.1016/j.gete.2024.100612","DOIUrl":"10.1016/j.gete.2024.100612","url":null,"abstract":"<div><div>Understanding and predicting potential failure mechanisms during the excavation and open drift stages of geological repository construction are among the crucial aspects of performance evaluation and safety assessment of nuclear waste storage facilities. The development of the Excavation Damage Zone (EDZ) and the generation of shrinkage-induced cracks during operational phases are prominent examples of failure mechanisms that can compromise the integrity of the repository systems. This study presents an integrated framework for investigating shrinkage-induced cracking of Opalinus Clay in niches and tunnels. To achieve this, the hybrid Finite Discrete Element Method (FDEM) is employed. The methodology incorporates a two-way staggered hydro-mechanical coupling scheme, where solid phase analysis relies on 2D FDEM and fluid flow is modeled using the nonlinear Richards’ equation and solved via Finite Volume discretization. To account for the effects of EDZ, characterized by a pronounced increase in hydraulic conductivity, a numerical simulation of tunnel excavation is first carried out. The resulting failure pattern around underground openings is then abstracted through the definition of an altered hydraulic conductivity field. Comparison of the numerical results with field observations demonstrates the framework’s ability to capture a wide range of failure mechanisms inherent in various stages of underground repository construction in Opalinus Clay.</div></div>","PeriodicalId":56008,"journal":{"name":"Geomechanics for Energy and the Environment","volume":"40 ","pages":"Article 100612"},"PeriodicalIF":3.3,"publicationDate":"2024-10-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142571511","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-10-28DOI: 10.1016/j.gete.2024.100613
A. Galgaro , R. Da Re , A. Carrera , E. Di Sipio , G. Dalla Santa
For the efficient design and implementation of a Ground Source Heat Pump (GSHP) system, the local subsoil stands as the core element. Alongside the conventional Thermal Response Test (TRT), recent research has developed improved approaches that garner more detailed information about ground thermal properties. One such technique is the fiber optic-based distributed thermal sensing. It relies on copper wires to thermally stimulate the ground, while optical fibers collect temperature variations over time along the cable. Another pioneering technology, the enhanced GEOsniff (produced by enOware GmbH), enables high-resolution, spatially-distributed representation of subsoil thermal properties along the Borehole Heat Exchanger (BHE) via wireless data transmission. This study compares and discusses data acquired through these two innovative techniques at the new campus for the humanities of the University of Padova, situated in Northern Italy's Eastern Po river plain. The findings are further juxtaposed with conventional TRT results, in terms of thermal conductivity and borehole thermal resistance. The thermal conductivity vertical profiles are also compared with direct measurements conducted on samples. These advanced techniques show promise in aiding the optimization of borehole length design, particularly in geological settings of heightened complexity.
地源热泵（GSHP）系统的有效设计和实施，当地底土是核心要素。除了传统的热响应测试 (TRT)，最近的研究还开发出了改进的方法，可以获得更详细的地热属性信息。其中一种技术是基于光纤的分布式热感应。它依靠铜线对地面进行热刺激，而光纤则沿着电缆收集温度随时间的变化。另一项开创性技术是增强型 GEOsniff（由 enOware GmbH 生产），它能够通过无线数据传输，沿钻孔热交换器（BHE）以高分辨率、空间分布方式显示地下热特性。本研究比较并讨论了在位于意大利北部东波河平原的帕多瓦大学人文新校区通过这两种创新技术获取的数据。研究结果与传统的 TRT 结果（热传导率和钻孔热阻）进行了进一步对比。热导率垂直剖面图还与对样品进行的直接测量结果进行了比较。这些先进技术有望帮助优化钻孔长度设计，尤其是在地质环境更加复杂的情况下。
{"title":"Comparison between new enhanced thermal response test methods for underground heat exchanger sizing","authors":"A. Galgaro , R. Da Re , A. Carrera , E. Di Sipio , G. Dalla Santa","doi":"10.1016/j.gete.2024.100613","DOIUrl":"10.1016/j.gete.2024.100613","url":null,"abstract":"<div><div>For the efficient design and implementation of a Ground Source Heat Pump (GSHP) system, the local subsoil stands as the core element. Alongside the conventional Thermal Response Test (TRT), recent research has developed improved approaches that garner more detailed information about ground thermal properties. One such technique is the fiber optic-based distributed thermal sensing. It relies on copper wires to thermally stimulate the ground, while optical fibers collect temperature variations over time along the cable. Another pioneering technology, the enhanced GEOsniff (produced by enOware GmbH), enables high-resolution, spatially-distributed representation of subsoil thermal properties along the Borehole Heat Exchanger (BHE) via wireless data transmission. This study compares and discusses data acquired through these two innovative techniques at the new campus for the humanities of the University of Padova, situated in Northern Italy's Eastern Po river plain. The findings are further juxtaposed with conventional TRT results, in terms of thermal conductivity and borehole thermal resistance. The thermal conductivity vertical profiles are also compared with direct measurements conducted on samples. These advanced techniques show promise in aiding the optimization of borehole length design, particularly in geological settings of heightened complexity.</div></div>","PeriodicalId":56008,"journal":{"name":"Geomechanics for Energy and the Environment","volume":"40 ","pages":"Article 100613"},"PeriodicalIF":3.3,"publicationDate":"2024-10-28","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142650683","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-10-24DOI: 10.1016/j.gete.2024.100611
Minhyeong Lee , Chang-Ho Hong , Ji-Won Kim , Jinwoo Kim , Jin-Seop Kim
Piping erosion presents a significant concern in engineered barrier system (EBS), contributing to performance uncertainties. However, the early-stage hydration and piping erosion characteristics of calcium-type bentonite under concentrated water inflow conditions are not fully understood. To address this gap, we examined early- and post-stage piping erosion in bentonite buffer materials. Specifically, we focused on the onset and evolution of piping channels with changes in the inflow pressure and their impact on buffer material integrity. Piping experiments were conducted using bentonite in block, granule, and powder forms under constant flow rate conditions. We analyzed the hydraulic-mechanical responses at the bentonite-cell interface, fluctuations in inflow water pressure, and eroded soil mass. Additionally, X-ray computed tomography imaging was utilized to assess the deterioration of buffer materials after piping. The results revealed that early-stage hydration-induced erosion behaviors are contingent upon the state of the bentonite buffer, with compacted blocks exhibiting predominant piping erosion. The rapid pressure buildup and breakthrough is essential in triggering piping erosion in the blocks, while the evolution of piping channels is influenced by the flow rate. Furthermore, severe cracks occurred along with the piping channels under reduced flow rate conditions, creating voids in the buffer amounting to 1.5–3.1 % of its initial volume. These findings provide insights into buffer-rock interfacial interactions in EBS, serving as the basis for in situ disposal experiments and the safe design of disposal repositories.
管道侵蚀是工程阻隔系统（EBS）的一个重要问题，也是造成性能不稳定的原因之一。然而，钙基膨润土在高浓度水流入条件下的早期水化和管道侵蚀特性尚未得到充分了解。为了填补这一空白，我们研究了膨润土缓冲材料的早期和后期管道侵蚀。具体来说，我们重点研究了随着流入压力的变化而出现的管道侵蚀及其对缓冲材料完整性的影响。我们使用块状、颗粒状和粉末状膨润土在恒定流速条件下进行了管道实验。我们分析了膨润土-池体界面的水力机械响应、流入水压的波动以及被侵蚀的土壤质量。此外，我们还利用 X 射线计算机断层扫描成像技术来评估管道铺设后缓冲材料的劣化情况。研究结果表明，早期水化诱发的侵蚀行为取决于膨润土缓冲区的状态，压实块体在管道侵蚀中占主导地位。压力的快速积累和突破是引发块体中管道侵蚀的关键，而管道通道的演变则受到流速的影响。此外，在流速降低的条件下，管道通道出现了严重的裂缝，在缓冲区内形成了占初始体积 1.5% 到 3.1% 的空隙。这些发现深入揭示了 EBS 中缓冲区与岩石的界面相互作用，为原位处置实验和处置库的安全设计提供了依据。
{"title":"Early and post-stage piping erosion in bentonite buffer materials exposed to groundwater inflow","authors":"Minhyeong Lee , Chang-Ho Hong , Ji-Won Kim , Jinwoo Kim , Jin-Seop Kim","doi":"10.1016/j.gete.2024.100611","DOIUrl":"10.1016/j.gete.2024.100611","url":null,"abstract":"<div><div>Piping erosion presents a significant concern in engineered barrier system (EBS), contributing to performance uncertainties. However, the early-stage hydration and piping erosion characteristics of calcium-type bentonite under concentrated water inflow conditions are not fully understood. To address this gap, we examined early- and post-stage piping erosion in bentonite buffer materials. Specifically, we focused on the onset and evolution of piping channels with changes in the inflow pressure and their impact on buffer material integrity. Piping experiments were conducted using bentonite in block, granule, and powder forms under constant flow rate conditions. We analyzed the hydraulic-mechanical responses at the bentonite-cell interface, fluctuations in inflow water pressure, and eroded soil mass. Additionally, X-ray computed tomography imaging was utilized to assess the deterioration of buffer materials after piping. The results revealed that early-stage hydration-induced erosion behaviors are contingent upon the state of the bentonite buffer, with compacted blocks exhibiting predominant piping erosion. The rapid pressure buildup and breakthrough is essential in triggering piping erosion in the blocks, while the evolution of piping channels is influenced by the flow rate. Furthermore, severe cracks occurred along with the piping channels under reduced flow rate conditions, creating voids in the buffer amounting to 1.5–3.1 % of its initial volume. These findings provide insights into buffer-rock interfacial interactions in EBS, serving as the basis for in situ disposal experiments and the safe design of disposal repositories.</div></div>","PeriodicalId":56008,"journal":{"name":"Geomechanics for Energy and the Environment","volume":"40 ","pages":"Article 100611"},"PeriodicalIF":3.3,"publicationDate":"2024-10-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142535955","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-10-22DOI: 10.1016/j.gete.2024.100610
A. Yehya , J. Basbous , E. Maalouf , T.S. Nemer
Reservoir induced seismicity is caused by stress changes due to the impoundment of water behind dams. In seismically active areas, the presence of critically located active faults makes the impoundment of water behind dams a seismic safety risk. Dam projects in Lebanon have become a soaring example of complacency and negligence that has overlooked the concerns for seismic safety raised over the projects and their high potential of inducing seismicity. In this paper, we use 2D and 3D fully coupled poroelastic modeling to assess the risk of dam impoundment on seismogenic faults located near dam sites in Lebanon. The coulomb failure stresses are calculated along the faults, and their variations are observed in relation to changes in pore pressures and normal stresses. In addition, the expected maximum earthquake magnitudes are computed along those faults. Our results show a high risk for reservoir induced seismicity on faults that are either underneath the reservoir or hydraulically connected to a fault beneath the reservoir. Consequently, the studied dams would present a serious hazard of induced seismicity in time where the region is already at high risk of destructive earthquakes after the catastrophic seismic events that struck Turkey and Syria on 6 February 2023 on the Eastern Anatolian Fault, which is connected to the Dead Sea Transform Fault that passes through Lebanon.
{"title":"Dam impoundment near active faults in areas with high seismic potential: Case studies from Bisri and Mseilha dams, Lebanon","authors":"A. Yehya , J. Basbous , E. Maalouf , T.S. Nemer","doi":"10.1016/j.gete.2024.100610","DOIUrl":"10.1016/j.gete.2024.100610","url":null,"abstract":"<div><div>Reservoir induced seismicity is caused by stress changes due to the impoundment of water behind dams. In seismically active areas, the presence of critically located active faults makes the impoundment of water behind dams a seismic safety risk. Dam projects in Lebanon have become a soaring example of complacency and negligence that has overlooked the concerns for seismic safety raised over the projects and their high potential of inducing seismicity. In this paper, we use 2D and 3D fully coupled poroelastic modeling to assess the risk of dam impoundment on seismogenic faults located near dam sites in Lebanon. The coulomb failure stresses are calculated along the faults, and their variations are observed in relation to changes in pore pressures and normal stresses. In addition, the expected maximum earthquake magnitudes are computed along those faults. Our results show a high risk for reservoir induced seismicity on faults that are either underneath the reservoir or hydraulically connected to a fault beneath the reservoir. Consequently, the studied dams would present a serious hazard of induced seismicity in time where the region is already at high risk of destructive earthquakes after the catastrophic seismic events that struck Turkey and Syria on 6 February 2023 on the Eastern Anatolian Fault, which is connected to the Dead Sea Transform Fault that passes through Lebanon.</div></div>","PeriodicalId":56008,"journal":{"name":"Geomechanics for Energy and the Environment","volume":"40 ","pages":"Article 100610"},"PeriodicalIF":3.3,"publicationDate":"2024-10-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142535953","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-10-22DOI: 10.1016/j.gete.2024.100609
Angran Tian, Xiaojie Tang, Jing Chen, Manman Hu
Microbially induced carbonate precipitation (MICP) is a promising method for transforming natural soils into a rock-like material, enhancing soil strength and creating an environmentally friendly engineered geomaterial for load-bearing purposes. Applying alternating current (AC) for enhancing precipitation including changing the crystalline form of the calcium carbonate precipitates appeals as a possible solution to break the upper limit of the unconfined compressive strength (UCS) of bio-treated specimens. To assess the viability of AC-assisted MICP, a series of experiments were designed and conducted under various combination of conditions. The UCS, calcium carbonate content and permeability of the bio-fabricated specimens were obtained to evaluate the treatment effectiveness of AC-assisted MICP. The results demonstrate that the UCS of the sand column exhibits a linear increase with the applied voltage from 10 V to 30 V (i.e., electric field strength from 0.91 V/cm to 2.73 V/cm). The UCS value of the bio-specimen reaches 9.4 MPa after 3 treatments at a concentration of 1.00 mol/L, a voltage of 30 V, and a frequency of 100 Hz. With the assistance of an AC electric field, the adverse impacts caused by high chemical concentrations in the MICP process can be mitigated. We report that a more uniform distribution of the calcium carbonate content of the treated specimen is obtained under an optimal AC frequency of approximately 100 Hz in the current series of experiments. The induced ion vibration under the action of AC results in a change in crystalline form and an increase in the amount and uniformity of crystals precipitated on the surface of the soil grains, supported by X-ray diffraction (XRD) patterns and scanning electron microscope (SEM) images. For reference, the energy consumption and the cost for increasing the UCS of the bio-treated specimen to 5 MPa is estimated at 375.86 kWh and 676.55 HK$ per cubic meter, respectively. The findings from our experimental investigation and analysis provide compelling evidence that utilizing AC electric field holds great potential for achieving an enhanced treatment effect of MICP and hence a stronger bio-soil.
{"title":"AC-assisted microbially induced carbonate precipitation for sand reinforcement: An experimental study","authors":"Angran Tian, Xiaojie Tang, Jing Chen, Manman Hu","doi":"10.1016/j.gete.2024.100609","DOIUrl":"10.1016/j.gete.2024.100609","url":null,"abstract":"<div><div>Microbially induced carbonate precipitation (MICP) is a promising method for transforming natural soils into a rock-like material, enhancing soil strength and creating an environmentally friendly engineered geomaterial for load-bearing purposes. Applying alternating current (AC) for enhancing precipitation including changing the crystalline form of the calcium carbonate precipitates appeals as a possible solution to break the upper limit of the unconfined compressive strength (UCS) of bio-treated specimens. To assess the viability of AC-assisted MICP, a series of experiments were designed and conducted under various combination of conditions. The UCS, calcium carbonate content and permeability of the bio-fabricated specimens were obtained to evaluate the treatment effectiveness of AC-assisted MICP. The results demonstrate that the UCS of the sand column exhibits a linear increase with the applied voltage from 10 V to 30 V (<em>i.e.</em>, electric field strength from 0.91 V/cm to 2.73 V/cm). The UCS value of the bio-specimen reaches 9.4 MPa after 3 treatments at a concentration of 1.00 mol/L, a voltage of 30 V, and a frequency of 100 Hz. With the assistance of an AC electric field, the adverse impacts caused by high chemical concentrations in the MICP process can be mitigated. We report that a more uniform distribution of the calcium carbonate content of the treated specimen is obtained under an optimal AC frequency of approximately 100 Hz in the current series of experiments. The induced ion vibration under the action of AC results in a change in crystalline form and an increase in the amount and uniformity of crystals precipitated on the surface of the soil grains, supported by X-ray diffraction (XRD) patterns and scanning electron microscope (SEM) images. For reference, the energy consumption and the cost for increasing the UCS of the bio-treated specimen to 5 MPa is estimated at 375.86 kWh and 676.55 HK$ per cubic meter, respectively. The findings from our experimental investigation and analysis provide compelling evidence that utilizing AC electric field holds great potential for achieving an enhanced treatment effect of MICP and hence a stronger bio-soil.</div></div>","PeriodicalId":56008,"journal":{"name":"Geomechanics for Energy and the Environment","volume":"40 ","pages":"Article 100609"},"PeriodicalIF":3.3,"publicationDate":"2024-10-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142538021","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-10-16DOI: 10.1016/j.gete.2024.100607
Lei Qin , Weikai Wang , Jun Matsushima , Haifei Lin , Siheng Lin , Zitong Xue , Xian Zhang
Exploring the heat transfer and deformation characteristics of coal bodies of different coal ranks during the freeze-thaw process is of significant importance for analyzing the fracture mechanism under the effect of liquid nitrogen (LN2). This experiment targets lignite, bituminite, and anthracite under both saturated and dry conditions. A real-time temperature-strain monitoring system was employed to observe the heat transfer and deformation characteristics of coal samples with different ranks throughout the freeze-thaw cycle. Additionally, a nuclear magnetic resonance system was utilized to examine the characteristics of pore damage before and after fracturing. The findings reveal: (1) During the freeze-thaw process, the absolute value of the temperature evolution rate for dry coal samples shows a negative correlation with coal rank, indicating a close link between temperature diffusion and intrinsic coal properties like oxygen content and porosity. (2) For saturated coal samples, the absolute value of the temperature change rate during freezing decreases as the coal rank increases, with the opposite trend observed during thawing. The phase change effect of water in fractures during freezing can enhance internal temperature diffusion in the coal body, while it acts as an inhibitor during thawing. (3) Based on the trend of strain fluctuations, the coal body deformation process during the freeze-thaw cycle can be segmented into seven stages, summarizing the general mechanisms of deformation failure. (4) Under saturated conditions, the amplitude of elastic deformation for each sample is negatively correlated with coal rank, with the sequence for dry coal samples being bituminite > anthracite > lignite. (5) The formation of a sealed space at the beginning of freezing is identified as a necessary condition for deformation during the freeze-thaw process, with the formation and strength of the sealed space depending on the temperature diffusion rate, moisture content, and inherent properties of the coal sample.
{"title":"Heat transfer-deformation characteristics and fracture damage analysis during LN2 freeze-thaw process in different rank coals","authors":"Lei Qin , Weikai Wang , Jun Matsushima , Haifei Lin , Siheng Lin , Zitong Xue , Xian Zhang","doi":"10.1016/j.gete.2024.100607","DOIUrl":"10.1016/j.gete.2024.100607","url":null,"abstract":"<div><div>Exploring the heat transfer and deformation characteristics of coal bodies of different coal ranks during the freeze-thaw process is of significant importance for analyzing the fracture mechanism under the effect of liquid nitrogen (LN<sub>2</sub>). This experiment targets lignite, bituminite, and anthracite under both saturated and dry conditions. A real-time temperature-strain monitoring system was employed to observe the heat transfer and deformation characteristics of coal samples with different ranks throughout the freeze-thaw cycle. Additionally, a nuclear magnetic resonance system was utilized to examine the characteristics of pore damage before and after fracturing. The findings reveal: (1) During the freeze-thaw process, the absolute value of the temperature evolution rate for dry coal samples shows a negative correlation with coal rank, indicating a close link between temperature diffusion and intrinsic coal properties like oxygen content and porosity. (2) For saturated coal samples, the absolute value of the temperature change rate during freezing decreases as the coal rank increases, with the opposite trend observed during thawing. The phase change effect of water in fractures during freezing can enhance internal temperature diffusion in the coal body, while it acts as an inhibitor during thawing. (3) Based on the trend of strain fluctuations, the coal body deformation process during the freeze-thaw cycle can be segmented into seven stages, summarizing the general mechanisms of deformation failure. (4) Under saturated conditions, the amplitude of elastic deformation for each sample is negatively correlated with coal rank, with the sequence for dry coal samples being bituminite > anthracite > lignite. (5) The formation of a sealed space at the beginning of freezing is identified as a necessary condition for deformation during the freeze-thaw process, with the formation and strength of the sealed space depending on the temperature diffusion rate, moisture content, and inherent properties of the coal sample.</div></div>","PeriodicalId":56008,"journal":{"name":"Geomechanics for Energy and the Environment","volume":"40 ","pages":"Article 100607"},"PeriodicalIF":3.3,"publicationDate":"2024-10-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142535857","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-10-16DOI: 10.1016/j.gete.2024.100606
Mouadh Rafai , Diana Salciarini , Philip J. Vardon
Numerous full-scale in situ tests have been conducted to assess the effect of thermal cycles on the pile response. However, those studies investigated the response of only precast and cast in-situ energy piles, with limited focus on the impact of the applied mechanical load on the pile response. This study presents the results of a field test conducted on a new type of energy pile, i.e. a displacement cast in-situ energy pile in multilayered soft soils, subjected to different fixed mechanical loads while undergoing simultaneous thermal cycles. Four tests were carried out, each corresponding to various axial loads ranging from 0 % to 60 % of the pile’s estimated bearing capacity. After applying the axial load on the pile head (0 %, 30 %, 40 %, or 60 % of the bearing capacity), the pile was subjected to up to ten thermal cycles. The highest magnitudes of thermal axial strains were observed near the pile top due to the lowest restraint provided by the made ground layer in all tests. Under zero (0 %) mechanical load, the thermal axial strains near the pile head were elastic and recoverable, while residual strain was observed near the toe. Under reasonable working mechanical loads (30 %, 40 %, or 60 %) residual strains were observed near both the pile head and the toe, with higher residual strains observed under higher mechanical loads. The results indicate that the cyclic thermal loadings could induce an increase in the compressive stress in the energy pile, attributed to the drag-down effects of the surrounding soil. The compressive stress induced by drag-down effects counteracts thermally induced tensile stress and thus leads to an insignificant effect on the energy pile during cooling. A limited impact of the shaft capacity was observed and was mainly attributed to the drag-down of the surrounding soil and thermal creep along the pile-soil interface.
{"title":"Full-scale in-situ tests on a displacement cast in situ energy pile: Effects of cyclic thermal loads under different mechanical load levels on pile stress and strain","authors":"Mouadh Rafai , Diana Salciarini , Philip J. Vardon","doi":"10.1016/j.gete.2024.100606","DOIUrl":"10.1016/j.gete.2024.100606","url":null,"abstract":"<div><div>Numerous full-scale in situ tests have been conducted to assess the effect of thermal cycles on the pile response. However, those studies investigated the response of only precast and cast in-situ energy piles, with limited focus on the impact of the applied mechanical load on the pile response. This study presents the results of a field test conducted on a new type of energy pile, i.e. a displacement cast in-situ energy pile in multilayered soft soils, subjected to different fixed mechanical loads while undergoing simultaneous thermal cycles. Four tests were carried out, each corresponding to various axial loads ranging from 0 % to 60 % of the pile’s estimated bearing capacity. After applying the axial load on the pile head (0 %, 30 %, 40 %, or 60 % of the bearing capacity), the pile was subjected to up to ten thermal cycles. The highest magnitudes of thermal axial strains were observed near the pile top due to the lowest restraint provided by the made ground layer in all tests. Under zero (0 %) mechanical load, the thermal axial strains near the pile head were elastic and recoverable, while residual strain was observed near the toe. Under reasonable working mechanical loads (30 %, 40 %, or 60 %) residual strains were observed near both the pile head and the toe, with higher residual strains observed under higher mechanical loads. The results indicate that the cyclic thermal loadings could induce an increase in the compressive stress in the energy pile, attributed to the drag-down effects of the surrounding soil. The compressive stress induced by drag-down effects counteracts thermally induced tensile stress and thus leads to an insignificant effect on the energy pile during cooling. A limited impact of the shaft capacity was observed and was mainly attributed to the drag-down of the surrounding soil and thermal creep along the pile-soil interface.</div></div>","PeriodicalId":56008,"journal":{"name":"Geomechanics for Energy and the Environment","volume":"40 ","pages":"Article 100606"},"PeriodicalIF":3.3,"publicationDate":"2024-10-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142535954","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-10-13DOI: 10.1016/j.gete.2024.100605
Roman Markiewicz , Adrian Thylbert Brunner , Johannes Pistrol , Dietmar Adam
The City of Vienna, as one of the largest public clients in Austria, initiated a research project to determine the load-bearing behavior of various foundation elements in typical Viennese soils. Numerous large-scale tests were carried out on bored piles, micro piles, anchors, and jet grouted columns. In addition, two energy piles were installed in different soil layers to investigate their behavior under mechanical and thermal loading in each soil layer separately. This paper discusses the energy pile in the Miocene sediments, which consist mainly of silty fine sand and some sandy silt. The energy pile – fully instrumented with strain gauges, extensometers, heat gauges and optical fiber sensors – was loaded for two and a half months. The mechanical load was kept constant throughout the thermal cycles to determine the response of the pile to thermal loads. The measured temperature data were used in numerical back-calculations to determine the thermal parameters of the soil layers and the concrete. Based on the measured strain and deformation data, the deformation behavior of the energy pile due to the thermal load was investigated. Finally, a static pile load test was carried out on the energy pile and the results are compared with those of the conventional reference piles installed in the vicinity, which have not been subjected to thermal loading. The test demonstrated that, after several weeks of cyclic thermal loading, the energy pile exhibited more favorable load-deformation behavior compared to conventional reference piles.
{"title":"Field investigations on the thermo-mechanical behavior of a partially activated energy pile in Miocene sediments","authors":"Roman Markiewicz , Adrian Thylbert Brunner , Johannes Pistrol , Dietmar Adam","doi":"10.1016/j.gete.2024.100605","DOIUrl":"10.1016/j.gete.2024.100605","url":null,"abstract":"<div><div>The City of Vienna, as one of the largest public clients in Austria, initiated a research project to determine the load-bearing behavior of various foundation elements in typical Viennese soils. Numerous large-scale tests were carried out on bored piles, micro piles, anchors, and jet grouted columns. In addition, two energy piles were installed in different soil layers to investigate their behavior under mechanical and thermal loading in each soil layer separately. This paper discusses the energy pile in the Miocene sediments, which consist mainly of silty fine sand and some sandy silt. The energy pile – fully instrumented with strain gauges, extensometers, heat gauges and optical fiber sensors – was loaded for two and a half months. The mechanical load was kept constant throughout the thermal cycles to determine the response of the pile to thermal loads. The measured temperature data were used in numerical back-calculations to determine the thermal parameters of the soil layers and the concrete. Based on the measured strain and deformation data, the deformation behavior of the energy pile due to the thermal load was investigated. Finally, a static pile load test was carried out on the energy pile and the results are compared with those of the conventional reference piles installed in the vicinity, which have not been subjected to thermal loading. The test demonstrated that, after several weeks of cyclic thermal loading, the energy pile exhibited more favorable load-deformation behavior compared to conventional reference piles.</div></div>","PeriodicalId":56008,"journal":{"name":"Geomechanics for Energy and the Environment","volume":"40 ","pages":"Article 100605"},"PeriodicalIF":3.3,"publicationDate":"2024-10-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142535956","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-10-05DOI: 10.1016/j.gete.2024.100603
Amulya Ratna Roul , Vikram Vishal
Understanding the thermomechanical response of rock at high temperatures is crucial for various energy applications such as underground coal gasification and geothermal systems. The study investigated the effects of temperature, mineral composition, and grain size on crack initiation (CI) and crack damage (CD) thresholds in Jodhpur sandstones using uniaxial compressive strength with acoustic emission, Brazilian tensile strength, and thermogravimetric analysis subjected to elevated temperatures. The study revealed distinct patterns in crack initiation stress threshold ratios (CISTR) and crack damage stress threshold ratios (CDSTR) influenced by mineral composition and grain size under temperature treatments. Ferruginous quartz arenite exhibited an inverse relationship between quartz content and crack initiation/damage stress thresholds, while siliceous quartz arenite and subarkose showed a positive correlation. The established variation is attributed to the differing grain boundary strengths among the minerals. Comparative analysis of crack thresholds with the minerals, excluding quartz and feldspar, revealed complex relationships with clay and other minerals. Finer-grained sandstones showed direct proportionality in CI and CISTR with clay content, while coarser sandstones exhibited an inverse relationship. Additionally, the study highlighted differential trends in toughness parameters and CISTR, emphasizing the role of grain size and heat-treatment conditions in governing stress thresholds. Significant chemical changes, including quartz phase shifts and kaolinite/muscovite dehydroxylation, occurred in sandstones at 500–600°C. The presence of kaolinite/hematite in ferruginous quartz arenite caused the increased mass loss in pure O2 due to kaolinite breakdown, while siliceous quartz arenite exhibited a greater mass loss in standard conditions. The findings suggest that quartz content does not consistently enhance rock strength under heat treatment, particularly in the presence of significant clay minerals, leading to an inverse quartz-rock strength relationship in ferruginous quartz arenites. The study provides valuable insights into the thermomechanical behavior of sandstones, which is crucial for assessing rock stability and durability in energy applications.
{"title":"Thermomechanical response and crack evolution of sandstone at elevated temperatures","authors":"Amulya Ratna Roul , Vikram Vishal","doi":"10.1016/j.gete.2024.100603","DOIUrl":"10.1016/j.gete.2024.100603","url":null,"abstract":"<div><div>Understanding the thermomechanical response of rock at high temperatures is crucial for various energy applications such as underground coal gasification and geothermal systems. The study investigated the effects of temperature, mineral composition, and grain size on crack initiation (CI) and crack damage (CD) thresholds in Jodhpur sandstones using uniaxial compressive strength with acoustic emission, Brazilian tensile strength, and thermogravimetric analysis subjected to elevated temperatures. The study revealed distinct patterns in crack initiation stress threshold ratios (CISTR) and crack damage stress threshold ratios (CDSTR) influenced by mineral composition and grain size under temperature treatments. Ferruginous quartz arenite exhibited an inverse relationship between quartz content and crack initiation/damage stress thresholds, while siliceous quartz arenite and subarkose showed a positive correlation. The established variation is attributed to the differing grain boundary strengths among the minerals. Comparative analysis of crack thresholds with the minerals, excluding quartz and feldspar, revealed complex relationships with clay and other minerals. Finer-grained sandstones showed direct proportionality in CI and CISTR with clay content, while coarser sandstones exhibited an inverse relationship. Additionally, the study highlighted differential trends in toughness parameters and CISTR, emphasizing the role of grain size and heat-treatment conditions in governing stress thresholds. Significant chemical changes, including quartz phase shifts and kaolinite/muscovite dehydroxylation, occurred in sandstones at 500–600°C. The presence of kaolinite/hematite in ferruginous quartz arenite caused the increased mass loss in pure O<sub>2</sub> due to kaolinite breakdown, while siliceous quartz arenite exhibited a greater mass loss in standard conditions. The findings suggest that quartz content does not consistently enhance rock strength under heat treatment, particularly in the presence of significant clay minerals, leading to an inverse quartz-rock strength relationship in ferruginous quartz arenites. The study provides valuable insights into the thermomechanical behavior of sandstones, which is crucial for assessing rock stability and durability in energy applications.</div></div>","PeriodicalId":56008,"journal":{"name":"Geomechanics for Energy and the Environment","volume":"40 ","pages":"Article 100603"},"PeriodicalIF":3.3,"publicationDate":"2024-10-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142424097","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"工程技术","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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